Control means for refrigerating system



1961 J. E. WATKINS 3 CONTROL MEANS FOR REFRIGERATING SYSTEM Filed 001:. 7, 1957 I I m LINE 2 571 M, 13 127 M 36% CONDENSER {,Z 1

LINE

CONOE N SE R RECEIVER INV EN TOR.

United States Patent 3,003,332 CONTROL MEANS FOR REFRIGERATING SYSTEM John E. Watkins, 307 Lake St., Maywood, H1. Filed Oct. 7, 1957, Ser. No. 688,721 6 Claims. (Cl. 62197) The invention relates to refrigerating systems generally and more particularly to large capacity or industrial refrigerating systems utilizing the compressive process for cooling.

Conventional refrigerating systems of the above general type require the maintenance of a relatively high pressure diiferential between the high and low sides of the system in order to provide the desired pressure drop through the valves which feed the evaporators. in the case of thermal feed valves, the standard rating is now 110 p.s.i.g. Other types of feel valves are comparahly rated. With suction pressure between 15 and 25 p.s.i.g. which is customary, condenser pressures from 149 to 165 p.s.i.g. are therefore required to obtain the necessary pressure drop at the feed valves.

As the pressure differentials for such systems are substantially fixed, the high condenser pressures must be maintained at all times. Thus, little, if any, advantage can be taken of seasonable or other temperature variations and power costs remain at the same high level throughout the year.

The inefliciency of the conventional refrigerating system operated in accordance with current practices has been appreciated and changes in construction and mode of operation have been suggested to eliminate some of the contributing factors. While improvements in efliciency have been realized, the proposed systems still fall short of attaining maximum eificiency. Thus, the provision of feed valves which allow overfeeding of the evaporator cooling coils at minimum condenser pressure allows a substantial reduction of condensing pressure with a consequent savings in power costs. Additional equipment is required, however, for collecting the excess liquid refrigerant passing through the evaporator coils and for returning it to the system for recirculation through the evaporator coils. A system of that type is disclosed in my Patent No. 2,570,241 issued March 25, 1952.

It has also been proposed to construct and arrange a refrigerating system so that condenser pressure can vary with seasonal or other temperature changes. A pump or other means is provided for boosting the pressure of the liquid refrigerant to the level required for operation with conventional feed valves. Such a system is disclosed in my copending application, Serial No. 570,620, filed March 9, 1956, now Patent No. 2,931,191.

With the above in view, a general object of the invention is to eliminate the objectionable features of prior refrigerating systems and to provide an improved system of extreme simplicity which is efficient and dependable and capable of producing maximum refrigera tion with a minimum expenditure of power.

Another object is to provide a refrigerating system in which it is only necessary to maintain a substantially constant but relatively low differential between liquid line and suction side pressures, condenser and other pressure being allowed to follow the weather" or to fiuctuate with ambient temperature changes to the end that Waste of power is eliminated or materially reduced.

Still another object is to provide a refrigerating system including controls operable to regulate the circulation of the cooling medium through the condenser in accordance with pressure prevailing in the condenser.

Other objects and advantages of the invention will become apparent from the following detailed description of the preferred embodiment and the modification illustrated in the accompanying. drawings in which FIGURE 1 is a diagrammatic view of a refrigerating system constructed in accordance with the present in vention.

FIG. 2 is a diagrammatic view of a modified form of the system.

-While a preferred form of the invention and a modification thereof have been shown in the drawings and will be described herein in detail, it is to be understood that this is not intended to limit the invention to the particular forms disclosed but, on the contrary, the intention is to cover all modifications, adaptations and alternative constructions falling within the spirit and scope of the invention as defined in the appended claims.

For purposes of illustration, the invention has been shown in FIG. 1 as incorporated in a refrigerating system suitable for year-around operation. This system, which is particularly adapted for use of one of the Freons, includes generally a compressor 10 driven by a motor M. The arrangement is preferably such that the capacity of the compressor or its operating speed can be varied through a wide range to meet the con-. ditions prevailing at any particular time.

'The compressor 10 is connected to discharge compressed refrigerant gas through a hot gas line 11 to a condenser 12 which reduces the temperature and liquefies the gas. The condenser 12 shown is of the conventional aircooled type, air being circulated over the cooling coils by a fan 13 driven by an electric motor M. It will be understood that the condenser 12 may be water cooled, if desired.

To insure an ample supply of liquid refrigerant at all times and to provide for the establishment and main tenance of optimum feed pressures, a receiver 15 of sufiicient capacity to accommodate seasonal require ments is provided. The refrigerant liquefied in the condenser 12 is transferred to the receiver by way of a' liquid line 16 and valve 17. The valve 17 may be a conventional high pressure float valve or other type of valve adapted to allow passage of liquid refrigerant from the condenser to the receiver 15 while isolating the latter from the high side of the system so that the pressure prevailing therein can be regulated independently. The purpose of this arrangement will be apparent as the description proceeds.

'Liquid refrigerant is supplied from the receiver 15 to an evaporator coil 20 or a series of such coils by way of a feed line 21 and feed valves 22 individual to the respective coils. Spent refrigerant is' returned from the evaporator coils to the compressor by way of a suction line 23.

In accordance with one aspect of the invention, substantial operating economies are achieved by providing for feeding the evaporating coils 20' with liquid refrigerant at substantially'lower pressure than has been considered practical heretofore. Thus, the feed valves 22, which may be of generally conventional construction, are modified to supply the required amount of refrigerant to the coils at a predetermined relatively low pressure drop, as for example, 15 p.s.i. instead of p.s.i., which is the present standard rating for such valves. The particular valves 22 shown are of the type known as thermal valves, each being automatically set in accordance with the demands of its associated evaporator coil under control of the temperature responsive means having a thermostatic sensing element or bulb 24 positioned to sense the temperature of the coil.

In the operation of the improved refiigerating system condensing pressure is allowed to rise and fall in accordance with changes in the ambient temperatures as reby the temperature variations of the cooling medium ciroulating through the-condenser. Provision .is made,

' however, for maintaining arninimum presure in the condenser sufficiently above receiver pressure to insure an adequate supply of liquid refrigerant under all temperature conditions. To accommodate such condenser pres- ;sure variations, provision is made for reducing receiver pressure to and maintaining it at the .level required for the operation of the feed valves. This may be either a predetermined :constant pressure or may be a constant refrigerant, provision is made for automatically regul'ating the circulation of cooling medium through the condenser in accordance with the system demands. In the refrigerating system shown in FIG. 1, such control is effected in accordance with condenser pressure by a control device 27 responsive to that pressure. The particular control device'illustrated is a pressure operated switch mechanism connected in the line L so as to shut ofi the current supply to the fan motor M when condenser pressure drops to a predetermined level. It will be evident that the control device 27 may be-utilized -to control a valve operator or pump when a'water cooled condenser is employed in the system.

The maintenance of a pressure in the liquid supply portion of the system diiferent fromthe condensing pressure, is made possible by provisionof the valve '17 in the liquid line 16 between the condenser and receiver. As indicated above, the valve 17 may be a conventional high pressure float valve of the type commonly used to feed evaporators. To guard against any possible back feed to the condenser due to an excessive drop in condensing pressure, a check valve 28 is also interposed in the liquid line 16. This valve further serves to isolate the receiver from the condenser. i

A typical operating procedure for a system constructed in accordance with the invention and using Freon 12 as the refrigerant gas is described below. It will be understood, of course, that the various pressure values-used are merely illustrative and that they may vary from the values stated.

As a starting point, it will be assumed that the feed valves 22 are designed (or modified if standard valves) to deliver their desired capacities at some predetermined relatively low pressure drop, for example, p.s.i. A's suming that 15 p.s.i. average suction pressure is required to maintain a desired temperature in the evaporator coils, a receiver pressure of around 40 p.s.i. will ordinarily be suflicient to overcome liquid line pressure drop and lift the refrigerant to the higher levels of the coils while providing the 15 p.s.i. drop through the feed lines 22. Valve 25 is accordingly set to maintain the receiver pressure at approximately 40 p.s.i.

It will be evident that a pressure somewhat higher than the receiver pressure will be required in the condenser to accommodate the pressure drop through the liquid line 16 and valves 17 and 28. Usually such pressure drop will not exceed '10 p.s.i., thus indicating a minimum condenser pressure of 50 p.s.i. res'su're responsive switching device 27 is therefore set to shut ofi the fan when condenser pressure drop approximately to that level.

The compressor 10 when operated at a rate to maintain l5 p.s.i. suction line pressure will more or less automatically adjust its output to supply the required volume of refrigerant gas to the condenser. 'In hot weather or when the ambient temperature or the temperature of the condenser cooling medium is relativelyhigh, condensing pressure may approach that of conventional systems, namely 165 p.s.i. 0n the other hand, when the ambient temperature falls, condensing pressure will decrease correspondingly and thus relieve the load on the compressor with a corresponding saving in power.

In real cold weather condensing pressure may fall below the minimum required to supply the receiver at 50 p.s.i. even though circulation of the cooling medium is interrupted. Under such conditions, liquid refrigerant collects inthe condenser coils, gradually reducing the active condensing surface area until condenser pressure builds up to the level required to discharge thecollected refrigerant to the receiver. It will be seen, however, that the condenser side of the system is allowed to follow the weather, that is, the condensing pressure is allowed to rise or ,fall' in accordance with the ambient temperature changes. Condensing pressure is raised above the level dictated by the prevailing temperature only for short intervals required to transfer collected refrigerant to the receiver when ambient temperature is extremely low. The-system is thus enabled to operate at its full capacity or in other words, to produce the maximum of refrigeration with a minimum expenditure of power.

The modified refrigerating system shown in FIG. 2 is adapted to operate in the same manner and with the same high efficiency shown in FIG. 1. As in the previously described system the compressor 10 discharges compressed refrigerant gas through the hot gas line 13. to the condenser 12. The condenser in this instance utilizes circulating water as the cooling medium, such water being supplied through a pipe 30 under control of a solenoid operated valve .31. Interruption of the water supply is efiected by closure of the valve 31 under control of the pressure responsive switch device 27 interposed in the power line L leading to the solenoid.

Refrigerant gas liquefied in the condenser 12 is delivered to the receiver 15 by way of the liquid line 16, the check valve 28 serving toisolate the receiver from he condenser to permit independent regulation of pressure in the liquid supply side of the system as before explained. In this case, the receiver discharges liquid rerrigerant by way of a liquid line 32 to a flash tank 33 which, in turn, supplies the feed lines 21 leading to the evaporating coils 20. Spent refrigerant is returned from the coils to the compressor by way of the suction line 23.

In accordance with the invention the pressure of the refrigerant supplied to the coils is maintained at a constant relatively low level by a pressure reducing valve 34. This valve is interposed in the liquid line .32 between the receiver and the'fiash tank. A control connection 35 with the suction line 23 enables the valve to maintain the required pressure differential for the functioning of the feed valves 36 in the feed lines 21, the feed valves being individual to the respective coils. The feed valves may be of any suitable character such as thermal valves similar to valve 22,-fioat valves or simply orifice valves. I

'The flash tank 33 may be of conventional construction provided with the usual level control device 37 for maintaining liquid level substantially constant. A vent valve 38 of suitable'type is provided for ventingflash gas from the tank to the suction line 23.

i In the operation of this system the condensing pressure is allowed to rise and fall in accordance with changesv in the temperature of the cooling medium which usually varies according to seasonal or other ambient temperature changes. A constant relatively low pressure differential is maintained across the feed valves 36 by the pressure control valve 34, thus insuring an adequate supply of refrigerant to the evaporator coils at all times. Furthermore, if condensing pressure tends to fall too low, circulation of the cooling medium is interrupted by the action of the pressure responsive device 27.

It will be evident from the foregoing that the invention provides a refrigerating system of novel and advantageous construction. By reason of the provision for regulating liquid line or feed pressure independently of condensing pressure, relatively low feed pressure may be used to advantage and the condensing pressure may be allowed to fluctuate through a wide range or to follow the weather. Full advantage is thus taken of seasonal or other ambient temperature variations and maximum refrigeration is produced with a minimum expenditure of power.

I claim as my invention:

1. In a refrigeration system having an evaporator coil and associated feed valve, a condenser cooled by a circulating cooling medium, a receiver connected to receive liquid refrigerant from the condenser and to deliver fluid to the evaporator coil through the feed valve, and a compressor connected to draw spent refrigerant in gaseous form from the evaporator coil and discharge it to the condenser for condensation to liquid form, the combination of valve means permitting flow of refrigerant only from the condenser to the receiver, and other valve means connected between said receiver and the intake side of the compressor operative to maintain the receiver pressure substantially constant and at a lower level than the condenser pressure.

2. In a refrigerating system, in combination, an evaporator, a feed valve connected to supply liquid refrigerant to said evaporator, a condenser, a receiver connected to receive liquid refrigerant from said condenser and to deliver it to said evaporator by way of said valve, a compressor, a suction line connecting said evaporator to the intake side of said compressor, a hot gas line connecting the discharge side of said compressor to said condenser, valve means interposed between said condenser and said receiver allowing flow of liquid refrigerant from the condenser to the receiver and preventing flow in the reverse direction, and valve means interposed between the receiver and the suction line cooperating with said first mentioned valve means for maintaining a constant diiferential between receiver and suction line pressures independently of the .condenser pressure required to maintain the supply of liquid refrigerant.

3. In a refrigerating system, in combination, an evaporator, a feed valve connected to supply liquid refrigerant to said evaporator, a condenser, power driven means for circulating a cooling medium through said condenser, a receiver connected to receive liquid refrigerant from said condenser and to deliver it to said evaporator through said feed valve, a compressor having its intake side connected by a suction line with said evaporator and its discharge side connected by a hot gas line with said condenser, a flash tank interposed between said receiver and said feed valve, a vent connection from said flash tank to said suction line for removing flash gas from the tank, and valve means operative in accordance with the pressure in said suction line to maintain the pressure of the liquid refrigerant in the flash tank at a predetermined relatively low level, said feed valve being dimensioned to pass sufficient refrigerant at said predetermined pressure to provide a desired degree of refrigoration.

4. In a refrigerating system including an evaporator, a feed valve dimensioned to deliver an adequate supply of liquid refrigerant to said evaporator with a relatively low pressure drop, a receiver connected for supplying liquid refrigerant to said said feed valve, a condenser exposed to seasonal temperature changes, a compressor operative to draw spent refrigerant gas from the evaporator and to discharge the gas under pressure to said condenser, said condenser operating to cool and Iiquefy the gas and to discharge it in liquid form to said receiver, means for reducing the pressure of the refrigerant supplied to said feed valve to a value effective to maintain said relatively low pressure drop across the valve, and means for isolating said receiver from said condenser so that condensing pressures may be varied as dictated by seasonal temperature changes without affecting the operation of the feed valve and evaporator.

5. In a refrigerating system including an evaporator, a feed valve dimensioned to deliver an adequate supply of liquid refrigerant to said evaporator with a relatively low pressure drop, a receiver connected to said feed valve for supplying liquid refrigerant thereto, a condenser cooled by a circulating fluid subject to seasonal and other temperature variations, a compressor operative to draw spent refrigerant gas from the evaporator and to discharge the gas to the condenser at a pressure effective to liquefy the same when cooled by the condenser conduit connections between said condenser and said receiver for delivering the liquid refrigerant to the receiver, means including a pressure reducing valve and a flash tank interposed between the receiver and the feed valve for reducing the pressure of the refrigerant supplied to said feed valve to a value effective to maintain said relatively low pressure drop across the valve, and a check valve interposed in said conduit connections operative to isolate said receiver from said condenser so that condenser pressure may be varied as dictated by the temperature of the condenser cooling fluid while the refrigerating action of the evaporator remains substantially constant.

6. In a refrigerating system including an evaporator, a feed valve dimensioned to deliver an adequate supply of liquid refrigerant to said evaporator with a relatively low pressure drop, a receiver connected to said feed valve for supplying liquid refrigerant thereto, a condenser cooled by a circulating fluid subject to seasonal and other temperature variations, a compressor operative to draw spent refrigerant gas from the evaporator and to discharge the gas to the condenser at a pressure effective to liquefy the same when cooled by the condenser, conduit connections between said condenser and said receiver for delivering the liquid refrigerant to the receiver, means for reducing the pressure of the refrigerant supplied to said feed valve to a value effective to maintain said relatively low pressure drop across the valve, and means for isolating said receiver from said condenser so that condenser pressure may be varied as dictated by the temperature of the condenser cooling fluid while the refrigerating action of the evaporator remains substantially constant.

References Cited in the file of this patent UNITED STATES PATENTS 1,691,286 Hiller Nov. 13, 1928 1,932,007 Baars Oct. 24, 1933 2,195,604 Taylor Apr. 2, 940 2,295,992 Gonzalez Sept. 15, 1942 2,500,688 Kellie Mar. 14, 1950 2,540,550 Schulz Feb. 6, 1951 2,621,487 Warren Dec. 16, 1952 2,626,506 Dickieson Jan. 27, 1953 2,761,287 Malkoif et a1. Sept. 4, 1956 2,764,476 Etter Sept. 25, 1956 2,807,145 Henderson Sept. 24, 1957 2,847,831 Carraway Aug. 19, 1958 

